The present invention relates generally to MR conditional electrode assemblies. Particularly, the present invention relates to needle and surface electrodes used in connection with Magnetic Resonance Imaging (MRI). More particularly, the invention relates to MR conditional needle and surface electrodes for use intraoperatively in operating room MRI suites and for long-term electroencephalogram (EEG) monitoring in Intensive Care Units (ICU's).
The terminology used for implants and devices in the MRI environment has evolved. For example, the term MRI or MR Compatible was used to describe a device that demonstrated neither a significant affect on the quality of the diagnostic information nor having its operations affected by the MR system. Currently, the MR task group of the American Society for Testing and Materials (ASTM) International developed a new set of terms. The electrodes of the present invention will thus be referred to as MR Conditional. The latter meaning a device that has demonstrated to pose no known hazards in a specified MRI environment with specified conditions of use.
Surface electrodes are used in the intensive care units (ICU) for patient monitoring. Needle electrodes may be used, for example, for patients that have been sedated prior to being in the ICU.
Regarding the prior art, needle and surface electrodes are commonly composed of stainless steel needles and recording discs or cones and the associated wires are typically composed of copper, tin, or carbon fiber leads. Stainless steel, tin, and copper are not MR conditional. The prior art does not teach or suggest a suitable MR conditional electrode structure. For example, Prior Art U.S. Pat. No. 5,445,162 discloses both sphenoidal “wire” electrodes made of silver and surface electrodes with a surface of gold or silver. However, the '162 patent does not disclose needle and surface electrodes constructed of materials comprising titanium, carbon fiber, carbon graphite, carbon impregnated polymers or ceramics.
One disadvantage of current needle and surface electrodes is that they must be removed before Magnetic Resonance Imaging (MRI) scans because the existing needles are not MR conditional. This disadvantage adds cost, considerable amount of time delays and potential inconsistencies recording pre versus post MR scan (due to the amount of time required to remove and then reposition the electrodes to the positions prior to the MR scan). The electrodes of the invention are constructed of lead-wires, needles and recording disc structures which are constructed of non-magnetic materials.
It is advantageous for caretakers to have electrodes that do not require the removal from the patient for MRI scans and then reapplied when the patient returns. It may, for example, require up to three hours to properly reposition the surface and needle electrodes on a patient.